1. Field of the Invention
The invention relates generally to a system for the coexistence between a plurality of wireless communications modules, and more particularly, to a system for the coexistence between a plurality of wireless communications modules sharing a single antenna.
2. Description of the Related Art
As shown in FIG. 1, a cellular phone may connect to a wireless local area network (WLAN) via a WLAN module thereof and simultaneously communicate with a BLUETOOTH handset (or a BLUETOOTH car audio, or others) through a BLUETOOTH module thereof. WLAN is typically implemented as an extension to wired local area networks (LANs) inside a building and is able to provide the last few meters of connectivity between a wired network and mobile or fixed devices. WLAN is based on the IEEE 802.11 standard. Most WLAN may operate in the 2.4 GHz license-free frequency band and have throughput rates of up to 2 Mbps. The 802.11b standard introduces direct sequence mechanism and provides throughput rates of up to 11 Mbps. The 802.11g standard operates at a maximum raw data rate of 54 Mbps, or about 19 Mbps net throughput. As shown in FIG. 1, an access point (AP) is connected to a LAN by an Ethernet cable. The AP typically receives, buffers, and transmits data between the WLAN and the wired network infrastructure. The AP may support, on average, twenty devices and have a coverage varying from 20 meters in an area with obstacles (walls, stairways, elevators etc) and up to 100 meters in an area with clear line of sight. BLUETOOTH is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs). Voice over internet protocol (VoIP) data from the Internet may be received through WLAN connection and vice versa. A cellular phone may transmit voice data through an established PAN to the BLUETOOTH handset and receive speech signals captured by a microphone of the BLUETOOTH handset via the BLUETOOTH module. The cellular phone may transmit digital music through the established PAN to be played back in the BLUETOOTH handset. WLAN and BLUETOOTH both occupy a section of the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, which is 83 MHz-wide. In light of cost issues as well as space used for component placement, modern electronic devices, such as cellular phones, Ultra-Mobile PCs (UMPCs) or others, are equipped with WLAN and BLUETOOTH modules sharing a single antenna instead of multiple antennas.
Referring to FIG. 2, for example, BLUETOOTH uses Frequency Hopping Spread Spectrum (FHSS) and is allowed to hop between 79 different 1 MHz-wide channels in a BLUETOOTH spectrum. WLAN uses Direct Sequence Spread Spectrum (DSSS) instead of FHSS. Its carrier remains centered on one channel, which is 22 MHz-wide. When the WLAN module and the BLUETOOTH module are operating simultaneously in the same area, as shown in FIG. 1, the single WLAN channel, which is 22 MHz-wide, occupies the same frequency space as 22 out of 79 BLUETOOTH channels which are 1 MHz-wide. When a BLUETOOTH transmission occurs on a frequency band that falls within the frequency space occupied by an ongoing WLAN transmission, a certain level of interference may occur, depending on the signal strength thereof. Due to the fact that the WLAN module and BLUETOOTH module share the same spectrum and also share a single antenna, avoiding interference therebetween is required.
FIG. 3 shows a diagram illustrating an operation conflict which may occur between a WLAN and a BLUETOOTH wireless communication service sharing a single antenna. In FIG. 3, the shared single antenna is switched between the WLAN and BLUETOOTH wireless communication services in a given time slot for transceiving data. Because the BLUETOOTH wireless communication service carries the audio data that requires real-time transmission, the BLUETOOTH wireless communication service has a higher priority over the WLAN wireless communication service. When a WLAN transceiving process takes place at the same time as a BLUETOOTH transceiving process, the WLAN transceiving process will be damaged. Referring to FIG. 3 again, the WLAN receiving operation (Rx operation) 30 occurs at a time slot when the BLUETOOTH wireless communication service remains idle. Therefore, the Rx operation 30 is performed without interference and an acknowledgement (ACK) message 31 is sent to the WLAN AP (such as the AP in FIG. 1) as a reply message after the Rx operation 30 is finished. Following the Rx operation 30, another WLAN Rx operation 32 occurs. The Rx operation 32 is also performed without interference because the BLUETOOTH wireless communication service is in the idle state. However, an ACK message 33 in response to the Rx operation 32 can not be replied to the WLAN AP, as the ACK message 33 will occupy the same time slot of a BLUETOOTH transmitting operation (Tx operation). In this case, the Rx operation 32 would be deemed as failed. In light of the failure, the WLAN AP would re-perform the Rx operation 32 with a lower rate in an attempt to successfully receive the ACK message. However, the re-performed Rx operation 32 (denoted as 34), which has a prolonged operation period, will be more likely to overlap with the BLUETOOTH transceiving time slot. This causes a further retry of the Rx operation 32, leading to a further decrement of the WLAN throughput. The performance degradation is caused by the inability of operating the WLAN and BLUETOOTH wireless communication services with a single antenna at the same time.